10S1 Lesson 5/6 - Experimental design

• Chemistry
• Secondary Education

Lesson 1 - What is IGCSE Chemistry?

<ol><li>Name appropriate apparatus for the measurement of time, temperature, mass and volume, including (a) stopwatches,(b) thermometers, (c) balances, (d) burettes, (e) volumetric pipettes, (f) measuring cylinders, (g) gas syringes</li><li>Suggest advantages and disadvantages of experimental methods and apparatus</li></ol>

Daily Review

Lightning Question

• State at least one insight you learned from the video you watched.
• Write it in your notebook.

The clock's ticking!

Think about these questions

• How much can you depend on measurements?
• Are all measurements trustworthy?
• How can you tell if it is only an approximation? 

The exact number of apples

Calibrated into divisions of 1 cm.

Calibrated into divisions of 0.1 cm.

Calibrated into divisions of 1 cm.

Calibrated into divisions of 0.1 cm.

What length is measured by Ruler A: 4.2 cm or 4.3 cm?

What length is measured by Ruler B: 4.27 cm or 4.28 cm?

REALISATIONS

• All measurements involve uncertainty.
• All measurement's last digit is always an estimate.
• The digits that you record when you measure something are called significant digits.

final, uncertain  digit

sure, certain digits

1

Watch and Learn

Worked example 1:

• 4.27 cm has three significant digits.
• 4 and 2 are certain (sure).
• 7 is the last uncertain digit.

Watch and Learn

Worked example 2:

• 5.201 g has four significant digits.
• _______, _______, and _____ are certain (sure).
• ________ is the last uncertain digit.

Watch and Learn

Worked example 3:

• 27.0 oC has ______ significant digits.
• _______ and _____ are certain (sure).
• ________ is the last uncertain digit.

2

Significant Digits

How many significant digits (SD) are there in:

• 9.776 g = 4 SD
• 23.4 kg = _______ SD
• 208 cm3 = 3 SD
• 45 094 mg = _______SD
• 0.0507 dm3 = 3 SD
• 0.000000000000071 mol = _______ SD
  
• 53 400 km = _______ SD or _____ SD

RULES for Significant Digits

(1) All non-zero digits are significant.

(2) All zeros in between non-zero numbers are significant.

(3) Zeros to the left of a value are NOT significant.

(4) Zeros to the right of a value may OR may not be significant.

(1) Identify the name of the apparatus.

(2) Read and write the measurement.

(3) Convert the measurement to a given unit.

(4) Identify the number of Significant digits.